Long Qt Syndrome
Informed by recognized medical guidance
Overview
Long QT syndrome (LQTS) is a rare condition that affects the heart's electrical system. In a healthy heart, each beat uses a small electrical signal. In LQTS, the heart takes a little longer than usual to 'recharge' between beats. This delay can sometimes trigger a very fast and unstable heart rhythm, which may cause fainting or, in the worst case, a cardiac arrest.
Key facts
- LQTS affects how the heart resets its electrical rhythm after every heartbeat.
- It is most often inherited, but certain medicines or mineral imbalances can also cause it.
- Many people with LQTS have no symptoms, but it can be found with an ECG (electrocardiogram).
- With proper treatment and follow-up, the risk of serious problems becomes much lower.
No, LQTS is considered rare. Around 1 in every 2,000 people may have it, but many do not know because they have no symptoms.
Anyone can have LQTS, but it is often diagnosed in children and young adults after a fainting spell. It can also appear in older adults, especially if certain medicines are involved.
Symptoms
- Fainting and not waking up
- No breathing or no pulse — call your local emergency number immediately and start CPR if you know how
- Fainting along with chest pain or severe shortness of breath
- A seizure that lasts more than a few minutes or repeats
- ⚠Fainting that you recover from quickly but has no clear cause
- ⚠Repeated dizzy spells or feeling you are about to faint
- ⚠Heart palpitations that last a long time or keep coming back
- ⚠If you already have LQTS and have any fainting episode, even if you recover
Common symptoms
- Fainting, especially during exercise, strong emotion, or sudden surprise
- Dizziness or lightheadedness
- Palpitations — a feeling that your heart is pounding, racing, or skipping beats
Symptoms in children
- Fainting while running, swimming, or playing sport
- Fainting when startled or during a strong emotional moment
- Shaking or seizure-like jerking that turns out to be caused by the heart, not a seizure
Symptoms in older adults
- Fainting or dizzy spells when starting a new medicine
- A fluttering or racing heartbeat that comes and goes
- Sometimes no symptoms at all, with the condition found on a routine ECG
Causes
Main causes
- A change in a gene that controls the electrical signals in the heart muscle cells — this faulty gene can be passed down from a parent
- Certain medicines, including some heart medicines, antibiotics, mental health medicines, and allergy medicines, can cause LQTS in some people
- Very low levels of potassium, magnesium, or calcium in the blood
- Other heart conditions that slow the heartbeat
Risk factors
- Having a close family member with LQTS
- A family history of unexplained fainting or sudden cardiac death at a young age
- Taking medicines that are known to prolong the QT interval — ask your doctor or pharmacist about the medicines you are on
- Having had an ECG that shows a longer than normal QT interval
When to see a doctor
See a doctor urgently if:
- After any unexpected fainting spell, especially if it happened during exercise or strong emotion
- If you have known LQTS and you notice new symptoms such as palpitations or dizziness
Book a routine appointment if:
- If a close family member has LQTS, even if you feel well
- If you have been told you have a long QT interval on an ECG but have not seen a specialist
- If you have a history of unexplained fainting and it has never been investigated
Diagnosis
A doctor will start by asking about your symptoms, family history, and any medicines you are taking. The main test is an ECG, which records the electrical activity of your heart. If the ECG suggests LQTS, you will usually be referred to a heart specialist for more tests.
Tests that may be done
- Resting ECG — a quick test that measures the electrical timing of your heartbeat
- Holter monitor — a portable ECG machine you wear for 24 to 48 hours to capture your heart rhythm over time
- Exercise stress test — records your heart rhythm while you walk on a treadmill or ride a bike
- Genetic blood test — looks for the specific gene changes that cause inherited LQTS
What to expect at your appointment
You will meet with a specialist who will explain the results in plain language and talk through what they mean for you and your family. If LQTS is confirmed, the doctor may suggest testing for family members, and together you will build a care plan.
Treatment
Treatment for LQTS is personal. The goal is to stop dangerous heart rhythms and reduce the chance of fainting or cardiac arrest. Some people only need to avoid triggers and have regular check-ups, while others need medicines or a small heart device.
Self-care at home
- Take any prescribed medicine exactly as your doctor tells you
- Always ask your doctor or pharmacist before starting any new medicine, including over-the-counter remedies
- Stay well hydrated and avoid becoming dehydrated
- Wear or carry medical identification that says you have LQTS
- Tell all doctors, dentists, and pharmacists about your condition
Medical treatments
For people who need more than lifestyle changes, doctors may prescribe a daily medicine to help keep the heartbeat steady and calm. If you have had more serious symptoms or are considered at high risk, a specialist may recommend a small device placed under the skin. These devices, such as a pacemaker or an implantable cardioverter-defibrillator (ICD), can sense and correct dangerous heart rhythms.
When is surgery considered?
Surgery is rarely the first option. In some severe cases where medicines are not enough, a specialist centre may offer a procedure to interrupt nerves that send fast signals to the heart. This is called left cardiac sympathetic denervation, and it is only considered for certain situations.
Living with this condition
Living with LQTS means learning what helps keep your heart calm and your life full. Many people continue to work, study, and enjoy family life. You may be advised to avoid competitive sports or certain intense activities if they raise your risk. Regular check-ups with your heart team are important.
Lifestyle tips
- Avoid known triggers, such as sudden loud noises if you have the type of LQTS that reacts to surprising sounds
- Limit or avoid alcohol and recreational drugs — these can affect your heart rhythm
- Avoid extreme heat and strenuous exercise until you have been assessed by your specialist
- Tell any doctor treating you — even for an unrelated problem — that you have LQTS
Diet and exercise
Eating a balanced diet and drinking enough fluids helps keep your body's mineral levels normal. A dietitian or doctor can advise about potassium, magnesium, and calcium. Exercise is often safe once you have had an exercise test, but some intense or competitive activities may not be suitable for you. Your specialist will give you clear guidance.
Mental health and emotional wellbeing
It is completely normal to feel anxious, worried, or sad after a diagnosis. Stress and strong emotions can sometimes trigger palpitations, so learning to manage stress is an important part of care. If you feel overwhelmed or depressed, talk to your doctor — they can connect you with counselling or other support. If you ever have thoughts of harming yourself, seek help immediately from your local emergency services.
Prevention
If LQTS is inherited, you cannot prevent the gene change itself. But you can prevent dangerous episodes by getting a proper diagnosis, avoiding known triggers, taking treatment, and staying in contact with your heart team. If the cause is a medicine or a mineral imbalance, correcting that may reverse the condition.
Vaccines
There is no vaccine that prevents LQTS. However, keeping your routine vaccinations up to date is still wise, because illnesses that cause fever or dehydration may put extra stress on the heart. Tell the person giving you a vaccine that you have LQTS before you receive it.
Screening programmes
If you are diagnosed with LQTS, close family members — such as parents, children, brothers, and sisters — may be offered an ECG and genetic testing. Screening can find LQTS in people who have no symptoms, which allows them to take steps to protect their heart.
Complications
If left untreated
- Dangerous heart rhythms that can cause sudden collapse
- Fainting-related injuries, such as falls or head injuries
- Cardiac arrest, which can be life-threatening without immediate emergency treatment
Long-term outlook
The outlook for people with LQTS is encouraging. With the right diagnosis, treatment, and follow-up, the risk of sudden death drops dramatically. Many people with LQTS live active, full lives. Your specialist can give you a clear and honest picture of what your own future may look like.
Find support
International organisations
Local organisations
- British Heart Foundation ↗ · United Kingdom
- Cardiac Risk in the Young ↗ · United Kingdom
External links open third-party websites. Ruqelo Health is not responsible for external content. Listing an organisation does not imply endorsement.
Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 31, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.